Hostname: page-component-848d4c4894-ttngx Total loading time: 0 Render date: 2024-05-21T06:54:59.844Z Has data issue: false hasContentIssue false
  • English
  • Français

Evolution of the streamwise vortices generated between leading edge tubercles

Published online by Cambridge University Press:  12 January 2016

Kristy L. Hansen ,
Nikan Rostamzadeh ,
Richard M. Kelso  and
Bassam B. Dally
Kristy L. Hansen*
Affiliation:
School of Computer Science, Engineering and Mathematics, Flinders University, Tonsley Campus, Adelaide, South Australia 5042, Australia
Nikan Rostamzadeh
Affiliation:
School of Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
Richard M. Kelso
Affiliation:
School of Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
Bassam B. Dally
Affiliation:
School of Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
*
†Email address for correspondence: kristy.hansen@flinders.edu.au
Get access Rights & Permissions [Opens in a new window]

Abstract

Sinusoidal modifications to the leading edge of a foil, or tubercles, have been shown to improve aerodynamic performance under certain flow conditions. One of the mechanisms of performance enhancement is believed to be the generation of streamwise vortices, which improve the momentum exchange in the boundary layer. This experimental and numerical study investigates the formation and evolution of these streamwise vortices at a low Reynolds number of $Re=2230$, providing insight into both the averaged and time-dependent flow patterns. Furthermore, the strength of the vortices is quantified through calculation of the vorticity and circulation, and it is found that the circulation increases in the downstream direction. There is strong agreement between the experimental and numerical observations, and this allows close examination of the flow structure. The results demonstrate that the presence of strong pressure gradients near the leading edge gives rise to a significant surface flux of vorticity in this region. As soon as this vorticity is created, it is stretched, tilted and diffused in a highly three-dimensional manner. These processes lead to the generation of a pair of streamwise vortices between the tubercle peaks. A horseshoe-shaped separation zone is shown to initiate behind a tubercle trough, and this region of separation is bounded by a canopy of boundary-layer vorticity. Along the sides of this shear layer canopy, a continued influx of boundary-layer vorticity occurs, resulting in an increase in circulation of the primary streamwise vortices in the downstream direction. Flow visualisation and particle image velocimetry studies support these observations and demonstrate that the flow characteristics vary with time, particularly near the trailing edge and at a higher angle of attack. Numerical evaluation of the lift and drag coefficients reveals that, for this particular flow regime, the performance of a foil with tubercles is slightly better than that of an unmodified foil.

JFM classification

Aerodynamics: Aerodynamics Flow Control: Flow Control Flow Control: Mixing enhancement
Type
Papers
Information
Journal of Fluid Mechanics , Volume 788 , 10 February 2016 , pp. 730 - 766
Copyright
© 2016 Cambridge University Press 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Agui, J. C. & Jiminez, J. 1987 On the performance of particle tracking. J. Fluid Mech. 185, 447–468.CrossRefGoogle Scholar
Andersen, J. D. Jr 2007 Fundamentals of Aerodynamics, 4th edn. McGraw-Hill.Google Scholar
ANSYS2014. ANSYS-CFX Solver Theory Guide. ANSYS CFX 14.0. Pennsylvania.Google Scholar
Barlow, J. B., Rae, W. H. Jr & Pope, A. 1999 Low-speed Wind Tunnel Testing. John Wiley & Sons Inc.Google Scholar
Custodio, D. 2007 The Effect of Humpback Whale-Like Leading Edge Protuberances on Hydrofoil Performance. Worcester Polytechnic Institute.Google Scholar
Etebari, A. & Vlachos, P. P. 2005 Improvements on the accuracy of derivative estimation from DPIV velocity measurements. Exp. Fluids 39, 1040–1050.Google Scholar
Favier, J., Pinelli, A. & Piomelli, U. 2012 Control of the separated flow around an airfoil using a wavy leading edge inspired by humpback whale flippers. C. R. Méc. 340, 107–114.Google Scholar
Fish, F. E. & Battle, J. M. 1995 Hydrodynamic design of the humpback whale flipper. J. Morphol. 225, 51–60.Google Scholar
Fish, F. E. & Lauder, G. V. 2006 Passive and active flow control by swimming fishes and mammals. Annu. Rev. Fluid Mech. 38, 193–224.CrossRefGoogle Scholar
Fouras, A. & Soria, J. 1998 Accuracy of out-of-plane vorticity measurements derived from in-plane velocity field data. Exp. Fluids 25, 409–430.CrossRefGoogle Scholar
Gad-el-Hak 2006 Flow Control: Passive, Active, and Reactive Flow Management. Cambridge University Press.Google Scholar
Hansen, K. L.2012. Effect of leading edge tubercles on airfoil performance. PhD thesis, The University of Adelaide.Google Scholar
Hansen, K. L., Kelso, R. M. & Dally, B. B. 2011 Performance variations of leading-edge tubercles for distinct airfoil profiles. AIAA J. 49, 185–194.Google Scholar
Hassan, E. R., Lau, T. C. W. & Kelso, R. M. 2007 Accuracy of circulation estimation schemes applied to discretised velocity field data. In 16th Australasian Fluid Mechanics Conference, Gold Coast, Australia. Australian Fluid Mechanics Society.Google Scholar
Johari, H., Henoch, C. W., Custodio, D. & Levshin, A. 2007 Effects of leading-edge protuberances on airfoil performance. AIAA J. 45, 2634–2642.Google Scholar
Johari, H. & Moreira, J. 1998 Direct measurement of delta-wing vortex circulation. AIAA J. 36, 2195–2203.Google Scholar
Langtry, R. & Menter, F. 2009 Correlation-based transition modeling for unstructured parallelized computational fluid dynamics codes. AIAA J. 47, 2894–2906.CrossRefGoogle Scholar
Lau, T.2010. The flow around a fish-inspired heaving and pitching hydrofoil. PhD thesis, The University of Adelaide.Google Scholar
Manolesos, M. & Voutsinas, S. G. 2014 Study of a stall cell using stereo particle image velocimetry. Phys. Fluids 26, 045101.Google Scholar
Miklosovic, D. S. & Murray, M. M. 2007 Experimental evaluation of sinusoidal leading edges. J. Aircraft 44, 1404–1407.CrossRefGoogle Scholar
Miklosovic, D. S., Murray, M. M., Howle, L. E. & Fish, F. E. 2004 Leading-edge tubercles delay stall on humpback whale (Megaptera novaeangliae) flippers. Phys. Fluids 16, L39.CrossRefGoogle Scholar
Morton, B. R. 1984 The generation and decay of vorticity. Geophys. Astrophys. Fluid Dyn. 28, 277–308.Google Scholar
van Nierop, E., Alben, S. & Brenner, M. 2008 How bumps on whale flippers delay stall: an aerodynamic model. Phys. Rev. Lett. 100 (5), 054502.CrossRefGoogle ScholarPubMed
Pedro, H. T. C & Kobayashi, M. H. 2008 Numerical study of stall delay on humpback whale flippers. In 46th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada.Google Scholar
Perkins, H. J. 1970 The formation of streamwise vorticity in turbulent flow. J. Fluid Mech. 44, 721–740.Google Scholar
Perry, A. E. & Hornung, H. G. 1984 Some aspects of three-dimensional separation, Part II: vortex skeletons. Z. Flugwiss. Weltraumforsch. 8, 155–160.Google Scholar
Raffel, M., Willert, C. E. & Kompenhans, J. 2007 Particle Image Velocimetry: A Practical Guide. Springer.CrossRefGoogle Scholar
Rostamzadeh, N., Hansen, K. L., Kelso, R. M. & Dally, B. B. 2014 The formation mechanism and impact of streamwise vortices on NACA 0021 airfoil’s performance with undulating leading edge modification. Phys. Fluids 26, 107101.CrossRefGoogle Scholar
Rostamzadeh, N., Kelso, R. M., Dally, B. B. & Hansen, K. L. 2012 The effect of undulating leading edge modifications on NACA 0021 airfoil characteristics. In 18th Australian Fluid Mechanics Conference, Launceston, Australia. Australian Fluid Mechanics Society.Google Scholar
Rostamzadeh, N., Kelso, R. M., Dally, B. B. & Hansen, K. L. 2013 The effect of undulating leading-edge modifications on NACA 0021 airfoil characteristics. Phys. Fluids 25, 117101.CrossRefGoogle Scholar
Skillen, A., Revell, A., Pinelli, A., Piomelli, U. & Favier, J. 2014 Flow over a wing with leading-edge undulations. AIAA J. 53, 464–472.Google Scholar
Stanway, M. J.2008 Hydrodynamic effects of leading edge tubercles on control surfaces and in flapping foil propulsion. Masters, Massachusetts Institute of Technology.Google Scholar
Stein, B. & Murray, M. M.2005. Stall mechanism analysis of humpback whale flipper models. Unmanned Untethered Submersible Technology (UUST), August 2005, Durham, NH.Google Scholar
Visser, K. D. & Nelson, R. C. 1993 Measurements of circulation and vorticity in the leading-edge vortex of a delta wing. AIAA J. 31, 104–111.Google Scholar
Watts, P. & Fish, F. E.2001 The influence of passive, leading edge tubercles on wing performance. In Proceedings of the Twelfth International Symposium on Unmanned Untethered Submersible Technology UUST, Lee, NH. Auton. Undersea Syst. Inst.Google Scholar
Weber, P. W., Howle, L. E., Murray, M. M. & Miklosovic, D. S. 2011 Computational evaluation of the performance of lifting surfaces with leading-edge protuberances. J. Aircraft 48, 591–600.CrossRefGoogle Scholar
Westerweel, J. & Scarano, F. 2005 Universal outlier detection for PIV data. Exp. Fluids 39, 1096–1100.CrossRefGoogle Scholar
Willert, C. E. & Gharib, M. 1991 Digital particle image velocimetry. Exp. Fluids 10, 181–193.CrossRefGoogle Scholar